Iowa remediation project

Manufactured gas plants (MGPs) produced gas from coal or oil for lighting, heating and cooking during the era prior to the availability of natural gas from interstate pipelines. Manufactured gas plants were active in Iowa from about the mid-1800s until the mid-1900s. 

Manufactured gas was a man-made product produced from coal or oil. The gas was manufactured by the destructive distillation of coal and oil. Destructive distillation is the decomposing of a material by heating in the absence of air (as opposed to burning), followed by recovery of products. The gas that was produced was stored on site in large cylindrical tanks, known as gas holders, before distribution to the community for heating, lighting and cooking.

As with many industrial processes, gas production typically created byproducts such as ash, cinders and coal tar. Coal tar was typically stored in underground structures at plant sites and was valuable as a fuel for heating at the manufactured gas plant but was also sold to others. When coal gas manufacturing plants were closed decades ago, the MGP by-products and residues often remained on site in underground structures. 

Coal tar is a thick black, brown or red-brown opaque liquids or solid materials produced during the gas production process. Coal tar was typically stored in underground structures at plant sites were sold to the chemical industry for the manufacture of dyes, medicines and perfumes and for use in creosote and road tar.

Coal tar and other MGP related residuals can contain polycyclic aromatic hydrocarbons (PAHs), such as naphthalene; volatile organic compounds (VOCs), such as benzene and toluene; and metals and other inorganic materials. PAHs are commonly found in the environment, because they form as a result of combustion, such as from vehicle exhaust. VOCs are often found in fuels and solvents. VOCs evaporates easily into the open air but could exist for a long time underground. More Information about these compounds is available from the federal Agency for Toxic Substances and Disease Registry (ATSDR) website.

Residuals, including tar, were found both on site and in an area adjacent to the former MGP sites. PAHs and VOCs associated with MGP-related residuals have been detected in soils and groundwater. The affected groundwater is not allowed to be used as a drinking or potable water supply.

There are many different chemical compounds in gas plant residues. Some have been found to cause adverse health effects under certain occupational conditions involving frequent or daily exposure. However, these same compounds are commonly found at lower levels throughout the environment from other natural and man-made sources.

Soil and groundwater tests and other studies previously conducted at the sites have found that gas plant residues are present below ground and there is little possibility for human contact except by digging. The community's drinking water is not affected by the MGP related residuals.
 

Black Hills Energy is proactively addressing potential environmental issues related to this MGP site to bring the site in line with current environmental standards. We are actively working with the IDNR and EPA to complete the remedial action in 2024 and 2025.

Black Hills Energy is coordinating the soil and groundwater sampling and the future remedial actions for the manufactured gas plant site with the Iowa DNR. The removal action goals for the remedial excavation were established based on risk-based objectives designed to be protective of people and the environment, in accordance with Environmental Protection Agency (EPA) guidance and approval.

The work is being conducted in accordance with applicable state and local requirements. The truck routes are designed to minimize traffic in the residential neighborhoods near the site. People in the vicinity may notice odors similar to roofing tar or moth balls if tar is encountered during the work. Although odors may become noticeable at times, they are generally not considered a health risk. Workers will be proactively using foaming agents to reduce the potential for odors within and near the site.

The site will be secured with fencing and access is limited to only properly trained workers. Work will be conducted primarily during daytime hours.
 

Yes. Black Hills Energy has successfully performed similar work in Nebraska resulting in regulatory closure of multiple MGP sites, primarily through the issuance of a No Further Action Certificate.